Keyboards, in particular keyboards for input of a PIN with keystrokes, as they are conventionally manufactured industrially at the present time, are usually constructed from a keyboard conductor plate and movable keys. By depressing the key a contact on the conductor plate is closed and information can generated and/or forwarded.
Since confidential data can be involved the keyboard must be protected against any tampering. For example, any recording of the inputted PIN by an attacker must be prevented.
In the case of keyboards with travel a possible attack consists in disassembly of the keyboard, the subsequent installation of a pressure-sensitive keyboard foil, and/or making direct contact with the key contacts and recording the PIN with the aid of evaluation electronics. Avoidance of this kind of problem by the use of keyboards with no travel that cannot be disassembled, such as touch screens, for example, does not satisfy all keyboard users. In particular a keyboard with travel is essential for blind people, since here the actuation of a key can best be achieved via the sense of touch.
A previous starting point to prevent any tampering with a keyboard with travel is the installation of appropriate housing switches; these are designed to prevent the disassembly of the keyboard, in that they initiate an alarm or the deletion of data in the event of interruption of particular contacts that are, for example, arranged between parts of the housing. However, an attacker can circumvent this precautionary measure by removing just the keys and installing evaluation electronics, without interrupting the contacts in the housing that are located underneath the keyboard. Here these contacts are designed to protect individual parts of the keyboard from disassembly.
It can therefore be seen as an object of the present invention to provide a keyboard, i.e. a security keyboard, which enables the removal of a key, or the disassembly of the keyboard, to be detected.